1. Field of the Invention
The present invention relates to a technology which estimates a state of charge of a battery.
2. Description of the Related Art
In devices each using storing devices such as a lithium secondary battery, a nickel-metal hydride battery, a lead battery, an electric double-layer capacitor, etc., e.g., a battery system, a distributed power storage system and an electric vehicle, a state detection device for detecting the state of the storing device has been employed to use the storing device with safety and effectively. As the state of the storing device, there are mentioned a state of charge (SOC) indicative of the extent to which it is being charged, or how dischargeable amount of charge remains, a state of health (SOH) indicative of how it is deteriorated, etc.
An SOC for a portable device and in a battery system of an electric vehicle or the like can be detected by integrating a discharge current from full charge and calculating the ratio of the amount of charge (remaining capacity) remaining in a storing device to the amount of charge (full capacity) chargeable to the maximum. In addition, the relation between a voltage (open circuit voltage) applied across a battery and the remaining capacity of battery is defined in a data table or the like in advance, and the current remaining capacity can also be calculated by referring to the data table or the like. Further, the state of charge can also be determined by using these techniques in combination.
A method of performing weighted addition to a charge characteristic determined from a discharge current and a charge characteristic determined from a battery voltage and deciding a weight at this time, based on a current value obtained from the output of a storing device and an internal resistance, thereby determining a state of charge has been described in JP-2011-85592-A.